This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for passerines
Lynx Edicions and BirdLife International will soon publish the second volume of the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.
The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.
Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.
The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 2 of the checklist (for passerines) will begin to be incorporated into the 2016 Red List update, with the remainder to be incorporated into subsequent Red List updates.
Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.
Slender-billed Cicadabird Coracina tenuirostris is being moved to the genus Edolisoma and split into Edolisoma tenuirostre, E. salomonis, E. remotum, E. grayi, E. obiense, E. mayerii, E. rostratum, E. monacha, E. nesiotis and E. inseperatum, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, Coracina tenuirostris (BirdLife species factsheet) was listed as Least Concern, on the basis that it did not approach the thresholds for listing as Vulnerable under any criteria. The pre-split species was characterised as generally uncommon, fairly common on Halmahera and common in the Trans-Fly region of New Guinea. On Yap it was described as rare, and uncommon in the Carolines generally, uncommon but widespread on Palau and the Solomons.
E. tenuirostre (as defined following the taxonomic change) is found from the Lesser Sundas, through the S Moluccas, Papua New Guinea through to E Australia. E. salomonis is restricted to the island of San Cristobal/Makira in the Solomon Islands. E. remotum is found throughout Melanesia, including the Admiralty Islands, Bismarks, New Britain, New Ireland and the Solomon Islands. E. grayi occurs throughout the N Moluccas. E. obiense occurs on the Banggai Islands, Obi and Bisa in the central Moluccas. E. mayerii is restricted to the Geelvink Islands and E. rostratum to Rossel Island in the Louisiade Archipelago. E. monacha is found only on Palau while in the Caroline Islands E. nesiotis is restricted to Yap and E. inseparatum is found only on Pohnpei.
The splitting up of this group of taxa leaves several new species with highly restricted ranges. The two Caroline Island taxa, E. nesiotis and E. inseparatum, along with E. salomonis, E. monacha and E. rostratum each possess an extent of occurrence (EOO) below 5,000km2, while Geelvink Cicadabird E. mayerii has an EOO of 11,000km2. The remaining taxa are not believed to approach the thresholds for listing as Vulnerable, and are proposed to be listed as Least Concern.
E.rostratum is restricted to Rossel Island in the Louisiade Archipelago, Papua New Guinea with a provisional EOO of 409 km2. The island retains significant forest cover although small-scale clearance is occurring in lowland areas, with less than 5% forest loss over the period 200-2014 (data from Hansen et al. 2013).
However, there do not appear to be any records of this species since Albert S. Meek collected the type specimen in 1898 (Sclater 1898). Were it to be known to be extant and present in similar densities to the pre-split species, then it is likely that the species would qualify as Endangered under category C2a(ii), on the basis of the single subpopulation, estimated small population size and inferred ongoing population decline.
But with no information on even whether the species is still present on the island, this species must initially be listed as Data Deficient.
If anyone has been to Rossel Island recently, please let us know!
E. nesiotis appears to have always been considered rare or uncommon and Engbring et al. (1990) estimated that the total population was just 273 birds, roughly equivalent to 180 mature individuals. The species is found widely across the island but with four times the density in forest compared to savanna (Engbring et al. 1990). It is still possible to locate the species during short visits to the island (e.g. Morris 2016), but there is no more recent population estimate or trend assessment.
Clearly this species is of concern, but it does not appear to have declined especially over recent times. Has the condition or extent of forested habitat on Yap changed in recent times? There is some tolerance indicated by the presence of the species throughout the island, but is there an underlying requirement for larger trees to maintain the population?
This appears to be a rare species with a very small but likely stable population. On this basis the species is proposed to be listed as Endangered under criterion D1.
Evidence for an ongoing decline in the population could qualify the species for listing as Critically Endangered under criterion C2a(ii). Several potential threats are poorly understood, for example rats are known to be on the island.
E. inseperatum is only found in the rugged interior of Pohnpei, where a reasonable area of original forest remains and the species still occurs, but at low densities: only 8 individuals were recorded at 247 survey stations between January and March 2012 (Oleiro 2014). An assessment of surveys in 1983 and 1994 indicated that encounter rates per hour had declined considerably over this time (although with too few registrations to be significant at the P< 0.05 level) (Buden 2000). Although the information is scant, there is sufficient to indicate that the species occurs at low density across a small potential total range and has declined considerably, though much of this decline likely happened prior to the most recent three generational period.
Engbring et al. (1990) estimated that the total population was 2,060 birds, with the highest densities occurring between 200-400 m above sea level. Given the apparent decline subsequent to this the population is here placed in the band 1,000-2,500 individuals, equating to 667-1,666 mature individuals which is rounded here to 600-1,700 mature individuals.
It is proposed that the species is listed as Endangered under criterion C2a(ii), on the basis that there are fewer than 2,500 mature individuals found in a single subpopulation suffering a continuing decline.
E. monacha occurs from Babeldaob to Peleliu with Palau. A newly calculated EOO for the species is 1460km2, and it has been characterized as uncommon but widespread (Taylor 2016b). The population of the species was estimated in 1991 at 12,642 (Engbring 1992), roughly equivalent to 8,300 mature individuals, and the relative abundance of the species was similar in 2005 compared to the 1991 survey, however the species was encountered less frequently on the Rock Islands (VanderWerf 2007). Several species were noted to be scarcer on the Rock Islands between the two species, but the causes are unknown (VanderWerf 2007). It is recognized that there is a moderate level of habitat loss on the islands that could be causing declines in the species, and the impact of introduced species has the potential to become very severe within a relatively short period.
It is proposed to list E. monarcha as Near Threatened, on the basis that it approaches the thresholds for listing as Vulnerable under criterion B1ab(iii,v) + B2ab(iii,v), noting that number of locations* is likely to be between 11 and 15 (with introduced predators as the principal threat) and that there may be a continuing decline in the area, extent and/or quality of habitat and number of mature individuals.
If there was clear evidence that the species is undergoing a continuing decline then the species would qualify for listing as Vulnerable under criterion B1ab(iii,v) + B2ab(iii,v).
E. salomonis is restricted to the island of San Cristobal (Makira) in the Solomon Islands, where it is considered fairly common (Taylor 2016a). It is not believed to approach the thresholds for listing as Vulnerable under any criteria, despite the restricted range and single subpopulation. Therefore it is proposed that the species be listed as Least Concern.
If there was evidence that the population was below 10,000 mature individuals and is undergoing an ongoing decline, then the species would qualify for listing as Vulnerable under criterion C2a(ii).
E. mayerii is found on the islands of Biak-Supiori and Numfor in the Geelvink Islands, West Papua. The species continues to be recorded by birders that visit Biak (e.g. Rheindt 2008) and is likely to be relatively common, if inconspicuous. However, a slow decline is suspected to be occurring owing to on-going habitat destruction. Forest on Biak is under heavy threat from logging and subsistence farming, but there are relatively large areas of forest remaining, especially in interior Supiori, and the species is assumed to be present in the 110km2 Biak-Utara protected area, which comprises virtually impenetrable forested limestone areas (Dekker et al. 2000, Bishop 1982 in Stattersfield et al. 1998, Wikramanayake et al. 2002). A great deal of the forest clearance on Biak took place during the last century however, with the suggestion that further large scale logging is presently not economically feasible (Wikramanayake et al. 2002). Therefore it is unlikely that declines in the area of habitat are likely to exceed the thresholds for listing under inferred population reduction (category A). In addition, given the apparent tolerance for a degree of habitat modification it is unlikely that the species would qualify for listing under the category B, geographic range size given that there are likely to be more than 10 locations* for the species in terms of habitat destruction, the principle threat. In addition it is not thought that the species approaches the thresholds for listing as Vulnerable under the population size criterion, given that there are at least two subpopulations and that on Biak is considered likely to consist of considerably more than 1,000 mature individuals. Consequently this species is proposed to be listed as Least Concern.
Comments are invited on these proposed categories and further information would be welcomed.
*Note that the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).
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